Hemozoin is a hydrophobic hem polymer, which is the detoxification product of the hem molecules found in the food vacuole of Plasmodium protozoa, and it can be produced by digestion of host hemoglobin by Plasmodium protozoa. As with CpG DNA, hemozoin acts as a ligand of Toll-like receptor 9. It is reported that the Toll-like receptor 9 is involved in innate immune responses to various pathogens, including Plasmodium. In other words, the immune system is activated in a MyD88-dependent manner when Toll-like receptor 9 recognizes a ligand.
The hemozoin synthesized from hemin chloride is referred to as “β-hematin” (see Slater et al., Proc. Natl. Acad., Sci., U.S.A., 88: 325-329, 1991).
It is reported that hemozoin activates spleen cells and dendritic cells of mice in vitro (see WO 2006/061965). It is also reported that hemozoin has adjuvant effects on the antibody production of ribonuclease A in mice (see U.S. Pat. No. 5,849,307).
In addition, it is reported that β-hematin has effects as an adjuvant of DNA vaccines (see Infect. Immun., July 2002; 70 (7): 3939-43). It is also reported that β-hematin functions as a ligand other than the TLR9 DNA molecule (a non-methylated DNA chain referred to as a so-called “CpG motif”) (see J. Exp. Med., Jan. 3, 2005; 201 (1): 19-25).
In addition, a vaccine adjuvant used in combination with an allergen vaccine containing β-hematin has been reported (see WO 2009/057763), in which hemin chloride is dissolved in a sodium hydroxide solution, a small amount of hydrochloric acid is added thereto, acetic acid is added at 60° C., so as to adjust the pH level to around 4.8, and the resultant is allowed to stand at room temperature overnight. Subsequently, a precipitate is obtained via centrifugation, and a weakly-basic sodium bicarbonate solution (pH: about 9), 2% of which is sodium dodecyl sulfate (SDS), is added to the precipitate, followed by washing for replacement with water. The resultant is then centrifuged for fractionation, and a fraction with an average particle size of 50 to 200 nm has potent adjuvant effects (see WO 2011/074711).